1. Field of Invention
This invention relates to a fluid-powered modular actuation system, more particularly to a self-feedback/balance, rotary actuation system. This system comprises a self-balanced, multiple-acting actuation module and a self-balanced, digital/non-digital, servo-positioning module. This system provides a rotary force to actuate and control different rotary valves with smaller size and higher accuracy and can be interfaced with different valves, power suppliers and control devices, those modules can be used separately with other control devices and valves.
2. Description of Prior Art
Conventional fluid-powered actuation systems comprise many components such as actuators, positioners and accessories, the components are designed and manufactured by different manufactures with different interfaces in compliance with different standards. In most cases, the components do not fit and work well with each other in terms of system performances, such as response time, accuracy of position and stability. In addition the conventional fluid-powered rotary actuation systems have many unsolved problems and disadvantages, such as heavy weight, high leakage, slow response, low accuracy, extra adapters, tubes and brackets for unmatched interfaces, lower reliability and lack of intrinsic safety features.
The most conventional rotary actuators are based on two types of linear-rotary movement conversion mechanisms; scotch-yoke and rack-pinion. They all have a common problem; unbalanced side loading forces, either on linear movement side or rotary movement side. As a result, the actuators have lower efficiency, heavy weight, high friction and high maintenance cost and are expensive to produce, and those problems largely prevent the actuators from being used in precision flow controls, fast operations or critical applications on medical equipment, aircraft and military services. On the other hand, the conventional positioners based on mechanical linkage/cam or balanced beam mechanisms have not changed over the years, those positioners have poor dynamic performances, such as slow response, large dead band, less accuracy and poor repeatability and they are not suitable for digital control applications, some positioners have been developed for those applications, but such positioners are either too expensive or not reliable.
In order to overcome the disadvantages of the conventional fluid-powered rotary actuation systems, many efforts have been made in the prior arts. There are four approaches to improve the conventional actuation systems in the prior arts, but those approaches work against each other within a limited scope.
The first approach is to simplify interfaces between actuators and positioners, U.S. Pat. No. 3,971,295 to Alan Richard Brine Nash (1976) disclosed an improved positioner with direct mounting on a rotary actuator, but there is no significant improvement in the positioner, on the other hand U.S. Pat. No. 4,882,977 to Toshio Himeno (1989) shows a systematical approach to mount a positioner directly on an actuator, but the system employing external conduit network between the positioner and the actuator is less compact and highly subject to breakage and external damage of fluid tubing.
The second approach is to ease consequences of the unbalanced side loading forces on actuators based on the scotch-yoke mechanism, since such mechanism has been used in fluid-powered actuation for years, many efforts were made, U.S. Pat. No. 3,261,266 to Hyman Ledeen (1966) shows an actuator with two cylinders or four cylinders, but the actuator employing external conduit network is extremely large and highly subject to breakage and external damage of fluid tubing, the yoke is subject to external corrosion and breakage, although the force on the yoke on four cylinder actuator is balanced but not efficient, the rod of pistons is under an unbalanced side loading force as the yoke moves away from 0 degree and has high leakage. U.S. Pat. No. 4,337,691 to Hisao Tomaru (1982) discloses a new design by easing consequence of unbalanced loading force on the linear side with bearings made out of lower friction materials but not on rotary side, the unbalanced side loading force on the yoke increases not only the friction between yoke and bearing, but also loading on the yoke which is required a much larger diameter to stand a combination of bending and torsion, on the contrary, U.S. Pat. No. 4,463,662 to Yukio Okuyama (1984) shows us a design to balance side forces on the yoke by employing a pair of pistons on opposite sides of yoke, but no effort was made to balance side loading forces on linear side.
The third approach is to improve performances and ease consequences of unbalanced side loading forces on actuators based on the rack-pinion mechanism. U.S. Pat. No. 1,667,559 to A. G. McCaleb (1928) shows us a typical example of rack-pinion double piston actuator, since then most efforts have been made to ease the consequence of unbalanced side loading force on the pistons, U.S. Pat. No. 4,167,897 to Alan D. Bunyard (1979) shows an improved rack-pinion actuator to ease the consequence of side loading force with extensions of pistons and bearings on the linear side, U.S. Pat. No. 4,203,351 to Heinz G. Schwind (1980) shows an improved rack-pinion actuator with three extensions to prevent the pistons to rotate and ease the consequence of unbalanced side force on pistons. In short, all the prior arts either fail to solve or did not recognize the unbalanced forces on both sides of linear-rotary conversion mechanism and rotary shaft leakage under side loading. In addition, the conventional actuators employ a pair of screws with nuts to control a rotation of output shaft either on linear side or rotary side through pressurized chamber, such structures not only create potential two leak paths and add unbalanced side force every time the screws are hit, but also increase the twist angle of output shaft and weaken output shaft as shown in U.S. Pat. No. 4,949,936 to Aurelio Messina (1990), moreover, the output shaft is axially constrained by two retaining rings, such arrangement not only requires a precision groove machining, but also increase difficulty of assembly with two grooves stack errors.
The fourth approach is to improve performances of the positioners, a typical example of the positioner is shown in U.S. Pat. No. 3,693,501 to Edward J. Ward et al (1972) and U.S. Pat. No. 3,971,295 to Alan Richard Brine Nash (1976), the positioner is based on a spool valve with mechanical linkages and cam feedback, while U.S. Pat. No. 3,565,391 to Benito C. Zannini (1971) and U.S. Pat. No. 4,509,403 to George W. Gassman (1985) disclose pneumatic positioners based on air relays with mechanical linkages and balanced beam, but they all need an extensive adjustment for setting a balanced point with a considerable moving parts in the mechanical linkages, the structures based on force-position feedback not only have a slow response time and high cumulative error, but also has inherently low reliability and large dead band and is susceptible to vibration and unstable, the positioner can not be used in services, such as high cycle, high vibration and quick opening or closing.
Even some newly developed positioners have some improvements with embedded microprocessors shown in U.S. Pat. No. 6,453,261 to Henry Boger et al (2002), but the fundamental control mechanism is still unchanged, the software route only can improve the performance with a limited scope, so at best, the positioning system has a novel diagnosis function, but the system is very complicated and expensive to produce, there is a great demand for a high reliable, digital-friendly positioner with high performance as good as or closed to the electronic positioner but at much lower cost. In fact, the most hydraulic positioners are based on conventional servo valves with flapper-nozzle structure shown in U.S. Pat. No. 4,922,964 to John H. Buscher (1990), the servo valve not only lacks self-feedback function, but also requires a filter for preventing fluid contamination and additional ports for fluid communication, moreover, an input signal generated by the torque motor is analog and expensive to be digitized.
So the fluid-powered actuation industry has long sought means of improving the performance of fluid-powered actuation system, eliminating the unbalanced side loading forces on both sides of linear-rotary conversion mechanism, reducing shaft leakage, response time and increasing reliability and accuracy with less cost.
In conclusion, insofar as I am aware, no fluid-powered actuation system formerly developed provides higher system performances with a modularization structure, less parts, highly efficient, versatile, reliable, easy manufacturing at lower cost, such system can be controlled by different type of input signals.